The present invention relates generally to the formation of optically transparent, scratch-resistant adherent coatings on substrates and, more particularly, to the formation of hard, hydrogenated diamond-like carbon coatings on substrates.
Hard, hydrogenated diamond-like carbon (DLC) films have received considerable attention due to their unique properties, which are close to those of diamond. Their high hardness, chemical inertness, optical transparency, and high electrical resistivity provide DLC films a strong potential for high-technological applications, such as hard, transparent optical coatings and protective scratch-resistant coatings. Currently, DLC films are prepared either from solid sources (vacuum plasma arc, ion beam sputtering, etc.) or from glow-discharge techniques using hydrocarbon arc, ion beam sputtering, etc.) or from glow-discharge techniques using hydrocarbon gases (direct current (dc)), radio frequency (rf), microwave and electron cyclotron resonance (ECR), with the substrates on the cathode). See, e.g., Y. Catherine DIAMOND AND DIAMOND-LIKE FILMS AND COATINGS, NATO ASI Series B, Vol. 266, Eds. R. E. Clausing et al. (Plenum Press, New York (1991), pages 193 ff.
Other techniques for generating DLC are mass-selected ion beam deposition, filtered vacuum arc deposition, plasma beam deposition, and plasma source ion implantation (PSII).
Unlike these methods, plasma immersion ion processing (PIIP), which combines the advantages of ion-beam-assisted deposition and plasma source ion implantation, is well-suited for producing conformal growth of DLC films. The PIIP technique is capable of producing solid films using high-density plasmas, at low substrate temperatures, and with independent control of ion energy. Non-line-of sight depositions are also possible.
In xe2x80x9cAmorphous Diamond Films,xe2x80x9d U.S. Pat. No. 5,763,087, which issued to Steven Falabella on Jun. 9, 1998, the generation of amorphous diamond films on cooled, negatively rf-biased substrates using a cathodic arc source for producing a carbon ion beam from a graphite cathode is described. Intrinsic stress of the amorphous diamond coatings is reported to have been significantly reduced (1-2 GPa), thereby providing a more durable coating on substrates. Amorphous diamond is an electrically insulating, inert, transparent allotrope of carbon. It lacks long-range ordered structure, contains little or no hydrogen, and is characterized by extraordinary hardness. By contrast, DLC is hydrogenated and softer than amorphous diamond.
Plastic materials such as PMMA (polymethyl methacrylate) are inexpensive, colorless and optically transparent materials. PMMA can be fabricated into optical components such for watch crystals or camera lenses, for commercial applications. The processing cost is low. However, PMMA is very soft and susceptible to scratching and thermal distortion.
Accordingly, it is an object of the present invention to provide a method for enhancing the surface hardness and wear resistance of substrates without deterioration of the optical properties thereof.
Another object of the invention is to provide a method for generating hard, well-bonded coatings on substrates having complex shapes at low temperature.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the method for forming an adherent, optically transparent, scratch-resistant diamond-like coating on a substrate hereof includes the steps of: applying a negative-pulsed bias voltage to the substrate, and immersing the biased substrate in a plasma containing ions simultaneously bearing carbon and hydrogen, whereby the ions are projected onto the surface of the substrate and form an optically transparent, scratch-resistant diamond-like coating on the surface thereof.
Preferably, the plasma is formed in a gas mixture of acetylene and an inert gas.
It is preferred that the inert gas includes argon.
In another aspect of the present invention, in accordance with its objects and purposes, the method for forming an adherent, optically transparent, scratch-resistant diamond-like coating on a substrate hereof includes the steps of: applying a negative-pulsed bias voltage to the substrate, and immersing the biased substrate in a plasma containing ions simultaneously bearing carbon and hydrogen, and ions bearing a dopant species, whereby the ions are projected onto the surface of the substrate and form an optically transparent, scratch-resistant diamond-like coating on the surface thereof.
Preferably, the plasma is formed in a gas mixture of acetylene, a doping gas and an inert gas.
It is preferred that the inert gas includes argon.
It is also preferred that the dopant species include boron and silicon and that the doping gas includes diborane (B2H6) or silane (SiH4), respectively.
Benefits and advantages of the present method include: (1) the maintenance of low substrate-processing temperatures which allows treatment of temperature-sensitive material such as plastics; (2) the use of rf inductive plasmas having high ion density which allows treatment of complicated shapes; and (3) the use of relatively low processing pressures which permits extensive plasma formation and the simultaneously processing of large areas or a large number of small components, in the production of optically transparent films having high hardness, excellent resistance to wear, and low stress.